Controlling the powertrain of a vehicle

ABSTRACT

The vehicle includes a powertrain having an axle having a first drive wheel and a second drive wheel. A first gearbox may couple a first power source to the first drive wheel, and a second gearbox may independently couple a second power source to the second drive wheel. And, a controller may be configured to initiate a gear shift in the first gearbox and the second gearbox at different times.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is continuation application of U.S. application Ser.No. 15/727,221, filed Oct. 6, 2017, which claims the benefit of U.S.Provisional Application No. 62/539,823, filed Aug. 1, 2017, thedisclosures of which are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

Embodiments of this disclosure relate to systems for controlling thepowertrain of a vehicle.

BACKGROUND

The powertrain of a vehicle refers to a group of components thatgenerate and deliver power to the road surface to propel the vehiclealong the road. In general, the powertrain includes a power source thatgenerates or provides power, and a transmission that transmits the powerto the drive wheels of the vehicle. In an electric vehicle, or a hybridvehicle operating in the electric mode, one or more electric motorsserve as the power source. In such vehicles, a battery provides power todrive the motors to produce torque. An inverter coupled to the motorsdirects current to the motors to produce torque in response to a torquerequest by a driver of the vehicle. The driver controls the position ofthe accelerator and brake pedals to request different amounts of torquefrom the motors. When the driver presses down on (or depresses) theaccelerator pedal, a controller detects the position of the pedal andsends a signal to the motors to increase the torque produced. When thedriver releases the accelerator pedal and/or presses down on the brakepedal, the controller sends a signal to the motors to decrease thetorque produced.

The transmission transmits the rotational power produced by the motorsto the drive wheels of the vehicle. The transmission incudes componentsthat convert the speed and torque produced by the motor to that desiredby the vehicle. One form of a transmission includes one or moregearboxes that use gears to provide speed and torque conversions betweenthe motors and the drive wheels. Typically, an input shaft inputs powerfrom a motor to a gearbox and an output shaft outputs the power from thegearbox to a drive wheel. The gearboxes include gears that selectivelyengage or disengage to increase or decrease the speed/torque between theinput and output shafts. Typically, a control unit of the powertraininitiates a gear shift in the transmission in response to drivingconditions.

In current transmissions with multiple gearboxes, gear shifting isinitiated in each gearbox simultaneously. Such simultaneous gearshifting may affect the performance of the vehicle in some cases.Embodiments of the current disclosure may address these limitationsand/or other problems in the art.

SUMMARY

Embodiments of the present disclosure relate to, among other things,devices and methods for controlling the powertrain of a vehicle. Each ofthe embodiments disclosed herein may include one or more of the featuresdescribed in connection with any of the other disclosed embodiments.

In one embodiment, a vehicle is disclosed. The vehicle includes apowertrain including an axle having a first drive wheel and a seconddrive wheel. A first gearbox may couple a first power source to thefirst drive wheel, and a second gearbox may independently couple asecond power source to the second drive wheel. The vehicle may alsoinclude a controller configured to initiate a gear shift in the firstgearbox and the second gearbox at different times.

In another embodiment, a method of controlling a power train of avehicle is disclosed. The method may comprise directing power from afirst power source to a first drive wheel of an axle through a firstgearbox, and independently directing power from a second power source toa second drive wheel of the axle through a second gearbox. The methodmay also include initiating a gear shift in the first gearbox and thesecond gearbox at different times.

In yet another embodiment, a vehicle is disclosed. The vehicle includesa powertrain comprising an axle having a first drive wheel and a seconddrive wheel. A first electric motor may be coupled to the first drivewheel via a first gearbox, and a second electric motor may beindependently coupled to the second drive wheel via a second gearbox.The vehicle may also include a controller configured to initiate a gearshift in the second gearbox after receipt of a signal indicating thatthe first gearbox has completed gear shifting.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate exemplary embodiments of thepresent disclosure and together with the description, serve to explainthe principles of the disclosure.

FIGS. 1A and 1B illustrate an exemplary electric bus according to thepresent disclosure;

FIG. 2 is a schematic illustration of an exemplary powertrain of the busof FIGS. 1A and 1B;

FIG. 3 is a schematic illustration of an exemplary power output of thepowertrain of FIG. 2; and

FIG. 4 illustrates an exemplary method of controlling the powertrain ofFIG. 2.

DETAILED DESCRIPTION

The present disclosure describes a system and method for controlling thetransmission of a vehicle. While principles of the current disclosureare described with reference to an electric vehicle, it should beunderstood that the disclosure is not limited thereto. Rather, thesystems and methods of the present disclosure may be used in any vehiclehaving a transmission with multiple gearboxes. As used herein, the term“electric vehicle” includes any vehicle or transport machine that isdriven at least in part by electricity (e.g., hybrid vehicles,all-electric vehicles, etc.).

FIGS. 1A and 1B illustrate an electric vehicle in the form of a bus 10.FIG. 1A shows the bus 10 with its roof visible, and FIG. 1B shows thebus 10 with its undercarriage visible. In the discussion below,reference will be made to both FIGS. 1A and 1B. Electric bus 10 mayinclude a body 12 enclosing a space for passengers. In some embodiments,some (or substantially all) parts of body 12 may be fabricated using oneor more composite materials to reduce the weight of bus 10. Withoutlimitation, body 12 of bus 10 may have any size, shape, andconfiguration. In some embodiments, bus 10 may be a low-floor electricbus. As is known in the art, in a low-floor bus, there are no stairs atthe front and/or the back doors of the bus. In such a bus, the floor ispositioned close to the road surface to ease entry and exit into thebus. In some embodiments, the floor height of the low-floor bus may beabout 12-16 inches from the road surface. In this disclosure, the term“about” is used to indicate a possible variation of ±10% in a statednumeric value.

Bus 10 may include a powertrain 30 that propels the bus 10 along a roadsurface. Powertrain 30 may include one or more electric motors thatgenerate power, and a transmission that transmits the power to a pair ofdrive wheels (e.g., wheels 24) of the bus 10. Batteries 14 may storeelectrical energy to power the electric motors of the powertrain 30. Insome embodiments, these batteries 14 may be configured as a plurality ofbattery packs 20 positioned in cavities located under the floor of thebus 10 (see FIG. 1B). In some embodiments, some or all of the batterypacks 20 may be positioned elsewhere (e.g., roof) on the bus 10. Thebatteries 14 may have any chemistry and construction. The batterychemistry and construction may enable fast charging of the batteries 14.In some embodiments, the batteries 14 may be lithium titanate oxide(LTO) batteries. In some embodiments, the batteries 14 may be nickelmetal cobalt oxide (NMC) batteries. It is also contemplated that, insome embodiments, the batteries 14 may include multiple differentchemistries. Some of the possible battery chemistries and arrangementsin bus 10 are described in commonly assigned U.S. Pat. No. 8,453,773,which is incorporated herein by reference in its entirety.

A charging interface 16 may be provided on the roof of the bus 10 tocharge the batteries 14. The charging interface 16 may includecomponents that interface with the charging head 120 of an externalcharging station 100 to charge the batteries 14. Some possibleembodiments of charging interfaces 16 that may be used for bus 10 aredescribed in commonly-assigned U.S. Patent Application Publication No.2014/0070767, which is incorporated by reference in its entirety herein.Alternatively or additionally, bus 10 may include other charginginterfaces, such as, for example, a charge port 22 (e.g., an electricsocket) that is configured to receive a charging plug and charge the bus10 using power from a utility grid. In such embodiments, the bus 10 mayadditionally or alternatively be charged by connecting the plug to thesocket. Some possible embodiments of charge port 22 that may be used forbus 10 are described in commonly-assigned U.S. patent application Ser.No. 15/589,281, filed May 8, 2017, which is incorporated by reference inits entirety herein.

FIG. 2 is a schematic illustration of an exemplary powertrain 30 of bus10. As illustrated in FIG. 2, powertrain 30 includes two electric motors(first motor 32A and second motor 32B), each independently coupled to adrive wheel 24 (first wheel 24A and second wheel 24B) of the bus 10through a gearbox 38 (first gearbox 38A and second gearbox 38B). Itshould be noted that the arrangement of the powertrain 30 illustrated inFIG. 2 is only exemplary, and other arrangements are possible. In theillustrated embodiment, the components of the power train 30 arepackaged such that these components extend linearly between two drivewheels 24 (i.e., first wheel 24A and second wheel 24B) of the bus 20.These drive wheels may be the pair of rear wheels in a rear-wheel drivebus, the pair of front wheels in a front-wheel drive bus, or a pair ofwheels between the front and rear wheels, for example, in a three-axlearticulated bus. However, this is not a requirement, and the componentsof the powertrain 30 may be arranged in any manner (such as, forexample, extending longitudinally along the length of the bus).

Although powertrain 30 is illustrated as having two electric motors 32,this is only exemplary. In general, the powertrain 30 may include anynumber of electric motors 32. For example, in some embodiments, a singleelectric motor 32 may provide power to all the drive wheels of the bus10 through a single gearbox or multiple gearboxes, and in someembodiments, multiple electric motors may provide power to each drivewheel through a single gearbox or multiple gearboxes. The electricmotors 32A and 32B may be permanent magnet synchronous motors (ACmotors) that operate using power from the batteries 14. In someembodiments, high voltage DC power from the batteries 14 may beconverted into 3-phase AC power using an inverter 34 (a single inverteror, as illustrated in FIG. 2, using a first inverter 34A and a secondinverter 34B) and directed to the motors 32. In some embodiments, a dualchannel inverter (e.g., a single inverter having different channels thatprovide power to, and control of, the motors independently) may be usedin place of two inverters (i.e., first inverter 34A and second inverter34B).

The first motor 32A and the second motor 32B may be the same orsubstantially similar to each other, the first gearbox 38A and thesecond gearbox 38B may be the same or substantially similar to eachother, and the first inverter 34A and the second inverter 34B may besimilar to each other. However, this is not a requirement, and in someembodiments, the first motors 32A may be different from the second motor32B (different torque rating, etc.), the first gearbox 38A may bedifferent from the second gearbox 38B (different gear ratios, etc.), andthe first inverter 34A may be different than the second inverter 34B(e.g., corresponding to the different motors, etc.). However, forsimplicity, in the discussion that follows, the first motor 32A isconsidered to be substantially similar to the second motor 32B, thefirst gearbox 38A is considered to be substantially similar to thesecond gearbox 38B, and the first inverter 34A is considered to besubstantially similar to the second inverter 34B. Therefore, only thefirst motor 32A, the first gearbox 38A, and the first inverter 34A, andtheir interconnection will be described herein. These descriptions alsoapply to the second motor 32B, the second gearbox 38B, and the secondinverter 34B, and their interconnections. In the discussion below, thefirst gearbox 38A (on the left side of FIG. 2) will be referred to asthe street-side gearbox, and the second gearbox 38B (on the right side)will be referred to as the curb-side gearbox.

First motor 32A rotates an input shaft that connects the first motor 32Ato the first gearbox 38A. An output shaft from the first gearbox 38Arotates the first wheels 24A directly (as illustrated in FIG. 2) or viaa speed reduction unit (e.g., connected between the first gearbox 38Aand the first wheel 24A) (not shown). In general, the torque output ofthe first motor 32A is proportional to the magnitude of the currentdirected into the first motor 32A from the first inverter 34A. Althoughthe first motor 32A is described as a permanent magnet synchronousmotor, as noted above, one or more other types of motors may be used inpowertrain 30.

First gearbox 38A may be a multi-speed gearbox which includes aplurality of gears (not shown) configured to switch between differentgear ratios to convert the rotational speed (and torque) of the gearboxinput shaft to several different speeds (and torques) of the gearboxoutput shaft. While, in general, any type of gearbox with any number ofgear ratios may be used in bus 10, in some embodiments, first gearbox38A may be a two-speed automated manual transmission that provides twogear ratios (e.g., a high gear and a low gear) using a set of planetarygears (or another type of gears). In the low gear, the speed of rotationof the gearbox output shaft may be lower than the speed of rotation ofthe gearbox input shaft. And, in the high gear, the speed of rotation ofthe output shaft may be greater than or equal to that of the inputshaft. As is known in the art, the planetary gears may include sun,ring, carrier and planetary gears, and a plurality of clutches adaptedto selectively couple several of the gears together to change the gearratio between the input shaft and the output shaft (of the first gearbox38A) based on instructions from a control unit 50.

The low and high gears may be activated by engaging (and/or disengaging)selected gears and clutches of the first gearbox 38A to obtain twodifferent gear ratios between the input and output shafts. The two gearratios convert the speed/torque of the gearbox input shaft to twodifferent speeds/torques of the gearbox output shaft. The first gearbox38A may be shifted between the low gear and the high gear automaticallyor manually, through the control unit 50 to suit different operatingstates of the bus. For example, during acceleration, based on theposition of the accelerator pedal 26 and the speed of the bus 10, thecontrol unit 50 may switch from the low gear to the high gear, andduring deceleration, based on the position of the brake pedal 28 and thespeed of the bus 10, the control unit 50 may switch the first gearbox38A from a high gear to a low gear. The first gearbox 38A may passthrough its neutral position when transitioning from the high gear tothe low gear, or when transitioning from the low gear to the high gear.When the first gearbox 38A is in its neutral position, the gearbox inputshaft and the gearbox output shaft of the first gearbox 38 aredecoupled, thus inhibiting power transfer to the first wheel 24A throughthe first gearbox 38A.

The first gearbox 38A may include one or more sensors 36 that indicateto the control unit 50 when a requested gear shift is complete. Thesesensors 36 may detect whether or not the gears of the first gearbox 38Aengage, and relay this data to the control unit 50 by way of a gearengagement signal. Any type of sensor configured to detect engagement ofthe gears may be used as sensor 36. In some embodiments, sensor 36 maybe a position sensor that detects whether (or not) the gears of thefirst gearbox 38A are in engagement based on a position of a gearshifting element (e.g., an element that moves the gears in engagement)of the first gearbox 38A. For example, in some embodiments, when theshifting element moves into a position corresponding to the engagementof the gears, a biased (e.g., by a spring) ball may descent into agroove in the shifting element to indicate gear engagement. In contrast,when the gears do not successfully engage (that is, do not engage oronly partially engages), the ball may not descent into the groove.Sensor 36 may also be a device that is not specifically made fordetecting engagement, but may nonetheless be used to infer gearengagement. For example, in some embodiments, sensor 36 may include anoutput shaft speed sensor that can be used to infer engagement when thedetected speed matches an expected speed (e.g., when the ratio of inputto output speed of the transmission is equal to the desired gear ratio).Based on the gear engagement signal from the sensor 36 (or anotherdevice), the control unit 50 may detect whether or not a requested gearshift is complete in a gearbox. For example, when the control unit 50instructs the first gearbox 38A to switch from its low gear to high gear(or vice versa), a gear engagement signal from sensor 36 of the firstgearbox 38A indicates to the control unit 50 that the requested gearshift is complete in the first gearbox 38A.

The control unit 50 may be an integrated master control system thatcontrols several operations of the bus 10. In some embodiments, controlunit 50 may be a distributed control system as known to people ofordinary skill in the art. That is, the functions of control unit 50 maybe divided between several different control systems (e.g., powertraincontroller, inverter/battery controller, vehicle controller, etc.) ofthe bus 10. As is known in the art, control unit 50 may include acollection of several mechanical, electrical, and integrated circuitdevices (for example, computational units, A/D converters, memory,switch, valves, actuators, fuses, etc.) that function collectively tocontrol the operation of the bus 10.

Among other functions, the control unit 50 may control the operation ofthe powertrain 30 based on several inputs from the bus 10. These inputsmay include a signal indicative of the position of the accelerator pedal26 and the brake pedal 28 of the bus 10. In use, when the driver of thebus 10 desires more torque (e.g., to climb a hill, accelerate, etc.),the driver may press down on the accelerator pedal 26. Pressing down theaccelerator pedal 26 (i.e., changing the position of the acceleratorpedal 26 from a less-depressed state to a more-depressed state) isindicative of a positive torque request from the driver. Similarly, whenthe driver wishes less torque, the driver may release the acceleratorpedal 26 (i.e., change the position of the accelerator pedal 26 from amore-depressed state to a less-depressed state) or press down on thebrake pedal 28 to produce a negative torque request. Position sensors(not shown), operatively coupled to the accelerator pedal 26 and thebrake pedal 28, may convert the position of these pedals to voltagesignals and provide these signals to the control unit 50. Based on thevoltage signal from these pedals (and other sensors, such as a speedsensor), the control unit 50 may send a torque request signal to thefirst and second inverters 34A and 34B to produce the requested torque.The torque request signal may include signals indicative of a particularvalue of current and/or voltage that, when directed to the first andsecond motors 38A, 38B will produce the desired torque.

In some embodiments, control unit 50 may also receive other inputsindicative of the operating conditions of the bus 10. These inputs mayinclude, among others, signals indicative of the state of charge (SOC)of the batteries 14, passenger load, a signal from an inclinometer thatis indicative of the grade of the road that the bus 10 is traveling on,signals from sensors that indicate the ambient weather conditions(temperature, precipitation, humidity, etc.). The torque request signalfrom the control unit 50 to the first and second inverters 34A, 34B maybe based on these signals and the driver requested torque. For instance,in some embodiments, when the state of charge of the batteries 14 isbelow a threshold value, the control unit 50 may decrease (or de-rate)the driver requested torque so that the torque output by the powertrain30 does not exceed a predetermined threshold value. Similarly, in someembodiments, when the temperature is below a threshold value, and/orwhen the passenger load is above a threshold value, and/or when the roadgrade is above or below a threshold value, the control unit 50 mayde-rate the requested torque.

As is known in the art, first inverter 34A may be an electronic device(or circuitry) adapted to convert direct current (DC) from the battery14 to alternating current (AC). In response to a torque request signalfrom the control unit 50, the first inverter 34 may activate IGBTs(insulated-gate bipolar transistors) or other switches to convert thedirect current from the batteries 14 to simulated AC current for thefirst motor 32A connected to the first inverter 34A. In someembodiments, the first inverter 34A may select the voltage and thefrequency of the AC current to produce the desired torque output(positive or negative). First motor 32A may include one or more sensors(speed sensor, torque sensor, etc.) configured to provide a signalindicative of the actual output torque of the first motor 32A to thefirst inverter 34A and/or the control unit 50. The first inverter 34Amay use the output of these sensors as feedback to modify (increase,decrease, etc.) the current directed to the first motor 32A to producethe desired torque output. Additionally or alternatively, in someembodiments, the first inverter 34A may include a sensor (currentsensor, etc.) that measures the current directed to the first motor 32A.Since, the torque produced by the first motor 32A is proportional to thecurrent directed to it, the first inverter 34A may use the detectedcurrent as a feedback signal for the actual torque output.

Control unit 50 may shift between the different gears of the firstgearbox 38A and the second gearbox 38B (i.e., between the high gear andthe low gear in the described embodiment) based on data indicative ofthe operating conditions of bus 10. The operating condition data mayinclude, among others, signals indicative of a desired speed, currentmotor speed, motor input current (or motor torque), etc. The desiredspeed may be determined based on operator input (for example, based onthe position of the accelerator and brake pedals 26, 28). Motor speedand motor input current data may be signals indicative of the currentspeed of the motors 32A, 32B, and the electric current input to thesemotors. Based on this data, the control unit 50 may energize one or moresolenoids to move actuators and/or shifting elements in each gearbox 38to bring different gears into, or out of, engagement to achieve therequested gear shift. As explained previously, a gear engagement signalfrom the sensor 36 of a gearbox indicates to the control unit 50 thatthe requested gear shift is complete in that gearbox.

With continuing reference to FIG. 2, in some embodiments, uponinstructions from the control unit 50, both the first gearbox 38A andthe second gearbox 38B performs a gear shift substantiallysimultaneously. That is, the control unit 50 may simultaneously instructboth the first gearbox 38A and the second gearbox 38B of the powertrain30 to shift from its low gear to its high gear, or vice versa. As eachgearbox 38A, 38B shifts between its low gear and high gear (or viceversa), it passes through its neutral position. In the neutral position,the input shaft of the gearbox 38A, 38B is decoupled from its outputshaft, and therefore, no torque is transmitted to the drive wheel 24A,24B connected to that gearbox 38A, 38B. In embodiments where both thefirst gearbox 38A and the second gearbox 38B shift gears simultaneously,both the gearboxes 38A, 38B may be in their neutral configurationsubstantially simultaneously, and therefore, for a brief period of time,the powertrain 30 may not transmit any torque to the drive wheels 24A,24B. For example, if the total torque requested by the operator (e.g.,based on the accelerator pedal 26 position, etc.) at the current time is200 Nm (Newton meters), the control unit 50 may direct the firstinverter 34A to produce 100 Nm of torque from the first motor 32A, andthe second inverter 34B to produce 100 Nm of torque from the secondmotor 32B. And, based on factors such as speed, etc., the control unit50 may also request each gearbox 38A, 38B to perform a gear shift (e.g.,from low gear to high gear). Since both the first and second gearboxesundergo gear shifting simultaneously, both will transition through itsneural position substantially simultaneously, and therefore, the torquedirected to the first and second drive wheels 24A, 24B will be zero.This sudden change in torque to both the drive wheels 24A, 24B maydetrimentally affect the performance (e.g., driver may feel a momentaryloss of power) and ride quality (e.g., felt as jolt to the passengers).Therefore, as explained further below, in some embodiments, the controlunit 50 may stagger the shifting of the gears in the first and secondgearboxes 38A, 38B.

In some embodiments, the control unit 50 may initiate a gear shift inone gearbox (e.g., first gearbox 38A) first, and the gear shift in othergearbox (i.e., second gearbox 38B) second. For example, in someembodiments, the control unit 50 may wait till it receives a gearengagement signal from sensor 36 (that indicates a successful completionof the gear shift) from the first gearbox 38A before it initiates thegear shift in the second gearbox 38B. In some embodiments, the controlunit 50 may wait for a predetermined period of time (100 millisecond,300 millisecond, 500 milliseconds, 700 milliseconds, etc.) afterinitiating gear shifting in the first gearbox 38A before initiating thegear shift in the second gearbox 38B. In the discussion below,performing gear shifting in one of the gearboxes of the powertrainfirst, and gear shifting in another gearbox of the powertrain second, isreferred to as split-shifting.

When split-shifting is performed in a powertrain 30, there will be adelay in time between when one of the drive wheels experiences zerotorque and the other drive wheel experiences zero torque (because eachgearbox transitions through its neutral state at different times).Although this will cause one of the drive wheels of the bus 10 totransfer zero torque while the other drive wheel is transferring torque,this is not considered to be a significant issue in a heavy-dutyvehicle, such as a bus, which has a relatively low power-to-weight ratioas compared to, for example, a passenger car (for example, a bus has apower-to-weight ratio of about 400 HP/30,000 lbs≅0.01 HP/lb as comparedto a high performance car which has a power-to-weight ratio of about 400HP/4000 lb≅0.1 HP/lb).

In general, the control unit 50 may initiate gear shift in any of thetwo gearboxes (i.e., the first gearbox 38A or the second gearbox 38B)first, and the other gearbox second. That is, the control unit 50 mayinitiate a gear shift in either the street-side or the curb-side gearboxfirst, and then initiate a gear shift in the other gearbox (after thegear shift in one gearbox is complete, after a predetermined amount oftime, etc.). In some embodiments, the control unit 50 may alternate thegearbox in which gear shifting is done first. For example, if gearshifting is first done on the curb-side gearbox now, gear shifting willbe first done on the street-side gearbox the next time. A counter in thecontrol unit 50 may keep track of which gearbox is gear shifted first.

In some embodiments, the gearbox which is gear shifted first may dependon the operating state (taking a left turn, taking a right turn, etc.)of the bus 10. For example, when the bus 10 is taking a left turn, thecontrol unit 50 may perform gear shifting first on the street-sidegearbox (i.e., the first gearbox 38A which will be the gearbox on theinner side of the turn), and then perform gear shifting on the curb-sidegearbox second (i.e., the second gearbox 38B.). And, when the bus 10 istaking a right turn, the control unit 50 may first perform gear shiftingon the curb-side gearbox, and then perform gear shifting on thestreet-side gearbox second. Performing gear shifting in this manner mayassist in making the turn by delaying the loss of power on the drivewheel which is on the outer side of the turn. The control unit 50 maydetermine the direction of the turn based on input from sensors (e.g.,sensors that detect steering position, wheel position, etc.). It is alsocontemplated that, in some embodiments, the curb-side gearbox is shiftedfirst when making a left turn, and the street-side gearbox is shiftedfirst when making a right turn. In some embodiments, the gear shifting(e.g., on both gearboxes) may be delayed until after the completion ofthe turn.

As explained previously, the control unit 50 controls the powertrain 30such that each electric motor 32A, 32B produces half the total requestedpower. That is, if the total requested torque is 200 Nm (based onoperator input via the accelerator pedal 26, brake pedal 28, currentspeed, etc.), the control unit 50 directs (via its inverter) the firstmotor 32A and the second motor 32B to each to output 100 Nm, so that thetotal power output by the powertrain 30 is 200 Nm. Duringsplit-shifting, in some embodiments, while the first gearbox 38A istransitioning through its neutral configuration and outputting zerotorque to the first drive wheel 24A, the second gearbox 38A willcontinue to transmit 100 Nm to the second drive wheel 24B. Thus, duringgear shifting the power output by the powertrain 30 may be momentarilydecreased.

In some embodiments, the control unit 50 will control the powertrain 30such that, during gear shifting in one gearbox, the power output of theother gearbox is adjusted so that the total power output by thepowertrain 30 remains substantially a constant. For example, in theexample above, when the total requested power is 200 Nm, the controlunit 50 directs the first motor 32A to produce the entirety of therequested torque (i.e., 200 Nm) when the second gearbox 38B is beinggear shifted, and directs the second motor 32B to produce 200 Nm oftorque when the first gearbox 38A is being gear shifted. After gearshifting is complete, the control unit 50 may instruct each of themotors 34A, 34B to produce half the requested torque.

FIG. 3 is a schematic illustration of the torque output of the drivewheels during an exemplary split-shifting. In FIG. 3, the solid lines(marked 70) represents the torque output of the drive wheel 24A(connected to the first gearbox 38A) and the dashed lines (marked 60)represents the torque output of the second drive wheel 24B (connected tothe second gearbox 38B). With reference to FIG. 3, at any instant oftime when the powertrain 30 is outputting 2 T Nm (e.g., about 400 Nm)(see 0-t₁ on the time axis), both first and second motors 34A, 34B willeach be producing about half of that torque, or T Nm (e.g., about 200Nm). During split-shifting, the control unit 50 may initiate gearshifting in the first gearbox 38A first (t₁-t₂ in the time axis), andinitiate gear shifting in the second gearbox 38B only after it receivesa signal indicting that the first gearbox 38A has successfully completedgear shifting (see t₂-t₃ in the time axis). As illustrated in FIG. 3,when gear shifting is occurring in the first gearbox 38A (t₁-t₂), thecontrol unit 50 increases the torque output of the second motor 32B toabout 2 T Nm to make up for the loss of power from the first wheel 24A.In some embodiments, during this time (i.e., t₁-t₂), the control unit 50may also reduce the torque output of the first motor 32A (i.e., themotor connected to the gearbox that is undergoing gear shifting) toensure that the torque output of the powertrain 30 does not increasemore than the requested value. When the control unit 50 receives asignal indicating that gear shifting of the first gearbox 38A iscomplete (e.g., at around time t₂), the control unit 50 may initiategear shifting in the second gearbox 38B and increase the power output ofthe first motor 32A to T_(X) (see FIG. 3) to make up for the loss oftorque from the second gearbox 38B. In some embodiments, during thistime (i.e., t₂-t₃), the control unit 50 may increase the torque outputof the first motor 32A to about 2 T Nm (i.e., T_(X)≅2 T Nm) to make upfor the loss of power from the second gearbox 38B.

In some embodiments, when gear shifting the second gearbox 38B (i.e.,t₂-t₃ in FIG. 3), the control unit 50 may adjust the torque output ofthe first motor 32A to a different value (for example, T_(X)=a×2 T Nm,where “a” may be a function of the gear ratio of the gearboxes) tomaintain a substantially constant torque at the wheels (and thus aconsistent drive feel). For example, in an embodiment, where each of themotors are producing T Nm of torque, and the control unit 50 issplit-shifting from a low gear (having, for example, a gear ratio of3:1) to a high gear (having, for example, a gear ratio of 1:1), thecontrol unit 50 may increase the torque output of the second motor 32Bto 2 T Nm (and, in some embodiments, decrease the torque output of thefirst motor 32A to zero) when gear shifting the first gearbox 38A (i.e.,between t₁-t₂ in FIG. 3). After the gear shifting of the first gearbox38A is complete, the control unit 50 may initiate gear shifting of thesecond gearbox 38B. During this time (i.e., between t₂-t₃ in FIG. 3),the control unit 50 may control the first motor 32A to produce a valueof torque equal to about (gear ratio of the low gear/gear ratio of highgear)×2 T=3/1×2 T Nm. Similarly, when shifting from the high gear to thelow gear, the control unit 50 may control the first motor 32A to producea torque value of about ⅓*2 T Nm when gear shifting the second gearbox38B (i.e., t₂-t₃). During this time, in some embodiments, the controlunit 50 may also instruct the second motor 32B to produce zero torque.After gear shifting is complete in the second gearbox 38B, the controlunit 50 may restore equal torque production from both motors 32A, 32B.

In the embodiments described above, the control unit 50 doubles thetorque output of the second motor 32B when the first gearbox 38A isundergoing gear shifting, and adjusts the torque output of the firstmotor 32A to value sufficient to maintain a substantially constanttorque at the wheels (i.e., to T_(X)) when the second gearbox 38B isundergoing gear shifting. In some embodiments, the control unit 50 mayincrease the torque output of each motor 32A, 32B based on the powerrating (e.g., torque output capacity) of each motor. For instance, inthe embodiment described with reference to FIG. 3, if the maximum torqueoutput capacity of each motor 32A, 32B is only 1.5 T Nm, the controlunit 50 may only increase the torque output of the first motor 32A to1.5 T Nm (or to a value less than 1.5 T Nm) when the second gearbox 38Bis undergoing gear shifting, and increase the torque output of thesecond motor 32B to a value less than or equal to 1.5 T Nm when thefirst gearbox 38A is undergoing gear shifting.

FIG. 4 illustrates an exemplary method 300 of controlling the powertrain30 of FIG. 2 using split-shifting. During operation, the control unit 50may control the first and second motors 32A, 32B (via inverters 34A and34B) to produce a torque of T Nm so that the powertrain 30 outputs atorque of 2 T Nm (step 310). When control unit 50 determines that gearshifting is desired (e.g., based on inputs to the control unit), gearshifting is initiated in the first gearbox 38A and the second motor 32Ais controlled to produce a torque output of about 2 T Nm (step 320).When the control unit 50 receives a signal from sensor 36 indicatingthat gear shifting in the first gearbox 38A is complete (step 330), gearshifting is initiated in the second gearbox 38B and the torque output ofthe first motor 32A is adjusted to about T_(X) Nm (step 340). Asexplained previously, in some embodiments, the value of T_(X) may beabout 2 T Nm. And, in some embodiments, to maintain a substantiallyconstant torque at the drive wheels during gear shifting, the value ofT_(X) may be determined based on, among other factors, the gear ratiosof the gear boxes. When the control unit 50 receives a signal indicatingthat gear shifting in the second gearbox 38B is complete (step 350), thetorque output of both the motors 32A, 32B are changed to T Nm (step360).

While principles of the present disclosure are described herein withreference to powertrains for electric buses, it should be understoodthat the disclosure is not limited thereto. Rather, the systems andmethods described herein may be employed in any type of electricvehicle. Also, those having ordinary skill in the art and access to theteachings provided herein will recognize additional modifications,applications, embodiments, and substitution of equivalents all fallwithin the scope of the embodiments described herein. Accordingly, theinvention is not to be considered as limited by the foregoingdescription. For example, while certain features have been described inconnection with various embodiments, it is to be understood that anyfeature described in conjunction with any embodiment disclosed hereinmay be used with any other embodiment disclosed herein.

We claim:
 1. A vehicle, comprising: a powertrain including: an axlehaving a first drive wheel and a second drive wheel; a first gearboxcoupling a first power source to the first drive wheel; a second gearboxindependently coupling a second power source to the second drive wheel;and a controller configured to initiate a gear shift in the firstgearbox and the second gearbox at different times.
 2. The vehicle ofclaim 1, wherein the controller is configured to initiate a gear shiftin the second gearbox after receipt of a signal indicating that thefirst gearbox has completed gear shifting.
 3. The vehicle of claim 1,wherein the first power source is a first electric motor and the secondpower source is a second electric motor.
 4. The vehicle of claim 3,wherein the vehicle is an electric bus.
 5. The vehicle of claim 1,wherein the controller is further configured to (a) increase a torqueoutput of the second power source and decrease the torque output of thefirst power source when the first gearbox is being gear shifted, and (b)increase the torque output of the first power source and decrease thetorque output of the second power source when the second gearbox isbeing gear shifted.
 6. The vehicle of claim 1, wherein the controller isconfigured to (a) increase a torque output of the second power source toa first torque value when the first gearbox is being gear shifted, and(b) adjust the torque output of the first power source to a secondtorque value when the second gearbox is being gear shifted, wherein thefirst torque value is different from the second torque value.
 7. Thevehicle of claim 1, wherein the controller is configured to (a) increasea torque output of the second power source to a first torque value whenthe first gearbox is being gear shifted, and (b) adjust the torqueoutput of the first power source to a second torque value when thesecond gearbox is being gear shifted, wherein the first torque value isdifferent from the second torque value.
 8. The vehicle of claim 7,wherein the first gearbox and the second gearbox both include at least afirst gear ratio and a second gear ratio, and wherein (c) the firsttorque value is equal to about a sum of the torque output of the firstpower source and the torque output of the second power source prior towhen gear shift is initiated in the first gearbox, and (d) the secondtorque value is equal to about a product of the first torque value and afunction of a ratio of the first gear ratio and the second gear.
 9. Thevehicle of claim 1, wherein the first gearbox and the second gearbox areboth a two-speed automated manual gearbox.
 10. A method of controlling apower train of a vehicle, comprising: directing power from a first powersource to a first drive wheel of an axle through a first gearbox;independently directing power from a second power source to a seconddrive wheel of the axle through a second gearbox; and initiating a gearshift in the first gearbox and the second gearbox at different times.11. The method of claim 10, wherein initiating a gear shift includesinitiating a gear shift in the second gearbox after receipt of a signalindicating that the first gearbox has completed gear shifting.
 12. Themethod of claim 10, wherein the first drive wheel is positioned on aleft side of the axle and the second drive wheel is positioned on aright side of the axle, and wherein initiating a gear shift includes (a)initiating a gear shift in the second gearbox after completion of a gearshift in the first gearbox when the vehicle is making a left turn, and(b) initiating a gear shift in the first gearbox after completion of agear shift in the second gearbox when the vehicle is making a rightturn.
 13. The method of claim 10, wherein the first gearbox and thesecond gearbox both include at least a first gear ratio and a secondgear ratio, and the method further includes increasing a torque outputof the second power source to a first torque value when the firstgearbox is being gear shifted, and adjusting a torque output of thefirst power source to a second torque value when the second gearbox isbeing gear shifted, wherein (c) the first torque value is equal to abouta sum of the torque output of the first power source and the torqueoutput of the second power source prior to when gear shift is initiatedin the first gearbox, and (d) the second value is equal to about aproduct of the first torque value and a function of a ratio of the firstgear ratio and the second gear ratio.
 14. The method of claim 10,wherein the first power source is a first electric motor and the secondpower source is a second electric motor.
 15. A vehicle, comprising: apowertrain comprising: an axle having a first drive wheel and a seconddrive wheel; a first electric motor coupled to the first drive wheel viaa first gearbox; a second electric motor independently coupled to thesecond drive wheel via a second gearbox; and a controller configured toinitiate a gear shift in the second gearbox after receipt of a signalindicating that the first gearbox has completed gear shifting.
 16. Thevehicle of claim 15, wherein the controller is further configured toincrease a torque output of the second electric motor when the firstgearbox is being gear shifted, and adjust the torque output of the firstelectric motor when the second gearbox is being gear shifted.
 17. Thevehicle of claim 15, wherein the controller is configured to (a)increase a torque output of the second electric motor to a first torquevalue when the first gearbox is being gear shifted, and (b) increase thetorque output of the first electric motor to the first torque value whenthe second gearbox is being gear shifted, wherein the first torque valueis equal to about a sum of the torque output of the first electric motorand the torque output of the second electric motor prior to when gearshift is initiated in the first gearbox.
 18. The vehicle of claim 15,wherein the first gearbox and the second gearbox both include at least afirst gear ratio and a second gear ratio, and wherein the controller isconfigured to (a) increase a torque output of the second electric motorto a first torque value when the first gearbox is being gear shifted,and (b) adjust the torque output of the first electric motor to a secondtorque value when the second gearbox is being gear shifted, wherein (c)the first torque value is equal to about a sum of the torque output ofthe first electric motor and the torque output of the second electricmotor prior to when gear shift is initiated in the first gearbox, and(d) the second torque value is equal to about a product of the firsttorque value and a function of a ratio of the first gear ratio and thesecond gear ratio.
 19. The vehicle of claim 15, wherein the firstgearbox and the second gearbox are both a two-speed automated manualgearbox.
 20. The vehicle of claim 15, wherein the vehicle is an electricbus.